Anyway... I haven't heard any confirmations about the used architecture, but the 580m has the same core count as the 485m as well as the same memory bus, seems to be a very similar architecture.

The 570m has more cores than the 470m, but my guess is that the architecture is similar as well.

The GTX 470m has a GF104 architecture, and it doesn't work flawlessly in the M15x... so I have my doubts about M15x getting these two new Nvidia working in the old faithful, but of course it needs to be tested to say anything reliable about the compatibility.

Since Dell uses the card I think chances are that it works... as far as the power consum is within 6970m levels, but I have some doubts because of the problems with the 470m.

The card's gonna cost a lot... I guess almost twice the price of a 6970m for a 580m.
Most interesting option imo is the 570m... would be great to get my hands on such a card and put it in the M15x... But it'll be similar priced to the 470m I guess, which was more expensive than a 6970m as well.

"The GTX 580M takes the place of the GTX 485M, and NVIDIA's bragging that it's the "fastest notebook GPU ever," capable, we're told, of besting the Radeon HD 6970M's tesselation performance by a factor of six." - Engadget
Hmm...if only...